Fluid bed reactors and their use in processes involving a molecular oxygen-containing gas with a solid catalyst for a heterogeneous gas phase reaction are known, for example from EP-A-0546677, EP-A-0685449 and EP-A-0847982.
EP-A-0546677 discloses a process for oxidising ethane to acetic acid in a fluidized bed reaction zone. In the example illustrated in EP-A-0546677, ethane is joined with a recycle stream containing water, CO, CO2, O2, ethylene and ethane and the combined stream is fed to the fluid bed reactor. A molecular oxygen-containing stream and steam are introduced separately into the fluid bed reactor. The hot oxidation products exit the top of the reactor.
EP-A-0685449 discloses a process for manufacturing vinyl acetate in a fluid bed reactor comprising feeding ethylene and acetic acid into the fluid bed reactor through one or more inlets, feeding an oxygen-containing gas into the fluid bed reactor through at least one further inlet, co-joining the oxygen-containing gas, ethylene and acetic acid in the fluid bed reactor while in contact with a fluid bed catalyst material to enable the ethylene, acetic acid and oxygen to react to produce vinyl acetate and recovering the vinyl acetate from the fluid bed reactor. According to EP-A-0685449, the oxygen may be added in pure form or as an admixture with inert gas such as nitrogen or carbon dioxide. Since the oxygen and hydrocarbons are not mixed until they are both inside the reactor, catalyst is present when they meet and reaction proceeds immediately, causing the oxygen partial pressure to drop. Thus, an advantage of feeding an oxygen-containing gas to the reactor through at least one further inlet in addition to the ethylene and acetic acid reactants is that it allows significantly higher levels of oxygen to be safely employed without a high inventory of flammable gas mixtures.
EP-A-0847982 discloses a process for the production of vinyl acetate by reacting at elevated temperature in a fluid bed reactor ethylene, acetic acid and an oxygen-containing gas in the presence of a fluid bed catalyst material characterised in that a liquid is introduced into the fluidised reactor for the purpose of removing heat therefrom by evaporation of the liquid. According to EP-A-0847982, the liquid introduced into the fluidised bed reactor may suitably be a reactant, an inert liquid or a product of the reaction, or a mixture of any two or more thereof. Thus, at least a part of the acetic acid reactant may be fed to the fluidised bed reactor in liquid form. A suitable product is said to be water, which is formed as a by-product of the reaction of ethylene, acetic acid and oxygen, because it has a relatively high latent heat of evaporation. It is stated therein that vinyl acetate product and/or acetaldehyde by-product may also be recycled and introduced in liquid form into the fluidised bed reactor.
According to EP-A-0847982, the liquid may be introduced into the fluidised-bed reactor by suitably arranged injection means. It is stated that a single injection means may be used or a plurality of injection means may be arranged within the fluidised bed reactor. According to EP-A-0847982, for introducing liquid into the fluidised catalyst bed, the number of injection means used is that number which is required to provide sufficient penetration and dispersion of liquid at each injection means to achieve good dispersion of liquid across the fluidised catalyst bed. A preferred injection means is said to be a nozzle or a plurality of nozzles which include gas-induced atomising nozzles in which a gas is used to assist in the injection of the liquid, or liquid-only spray-type nozzles. According to EP-A-0847982, liquid may be introduced with the ethylene and/or oxygen-containing gas and/or recycle gas fed to the fluidised bed reactor suitably by bubbling the ethylene and/or oxygen-containing gas and/or recycle gas through the liquid prior to its introduction into the reactor. In a further alternative, it is stated that liquid may be pumped into the area of the grid plate forming an essential component of a fluid bed reactor where contact with incoming ethylene and/or oxygen-containing gas and/or recycle gas would propel the liquid upwards into the fluidised catalyst bed. In yet a further alternative, it is stated that liquid may be pumped into the reactor via a sparge bar or bars, optionally with one or more of the gaseous feeds.
According to EP-A-0847982, the nozzle or nozzles may be located in the reactor grid or in the reactor walls above the grid.
EP-A-0985655 discloses a fluid bed process for the production of vinyl acetate which comprises feeding ethylene, liquid acetic acid and an oxygen-containing gas into a fluid bed reactor in which the amount of co-promoter is up to 6% by weight of the catalyst. It is stated therein that the acetic acid is introduced into the reactor in liquid form, optionally with some acid in the vapour form and that the liquid acetic acid may be introduced into the fluid bed reactor by any suitable injection means, for example a nozzle which may be a gas-induced atomising nozzle or liquid-only spray-type nozzles. It is also stated therein that one or more nozzles may be used and that additionally, recycled acetic acid may be introduced into the reactor either pre-mixed with the crude acetic acid or using a separate injection means
In the examples illustrated in EP-A-0985655, fresh acetic acid from storage (1) and recycle acetic acid are pumped together with some recycle gas (3) to twin fluid nozzle within the fluid bed (2). The remainder of the recycle gas feed (3), fresh ethylene (4) and oxygen (5) enter the plenum and through a sintered plate into the reactor. Fresh oxygen (6) may be fed directly into the fluid bed. A freeboard section is provided for disengaging the catalyst (7). The gaseous products exit the reactor through exit (8) through sintered filter elements (not shown).
There is a need for an improved process and apparatus for fluid bed heterogeneous gas-phase reactions in which at least one gas and at least one liquid are introduced to a fluidised bed of catalyst.